Optoelectronic Oscillators

Abstract

Without the need of any clock source, an optoelectronic oscillator (OEO) enables to simultaneously generate a high‐repetition‐rate optical clock/pulse train with low jitter and a microwave clock with high spectral purity, and it can be employed to further perform signal processing including data generation, pulse shaping, and clock recovery. Therefore, it becomes the center of attention in the microwave photonic technical area. Numerous techniques have been proposed to reduce the single‐sideband (SSB) phase noise and to improve the frequency stability of the OEO. In this article, a historical review of OEOs including different constructing methods and functionalities is introduced. Subsequently, a Mach–Zehnder modulator (MZM)‐based OEO at 40 GHz is focused to implement a synthesizer‐free 40 Gbit/s return‐to‐zero binary phase‐shifted‐keying (RZ‐BPSK) data generator. As a result, the 40 GHz microwave clock with a Q ‐factor of up to 2 × 10 8 is observed, and its SSB phase noise can be suppressed to −120 dBc/Hz at 100 kHz frequency offset. Moreover, its spectral quality is almost independent of the intraloop fiber‐induced radio‐frequency (RF) power fading. In addition, the delivered optical RZ carrier with a pulse on/off extinction ratio (ER) of 7.7 dB, a pulse width of 10.5 ps, and a timing jitter of 150 fs is particularly suitable for 40 Gbit/s RZ‐BPSK data transmission. At a requested bit error rate (BER) of 10 −9 , a back‐to‐back receiving power sensitivity of −16.3 dBm is observed, which indicates a power penalty of 4 dB after 25 km single‐mode‐fiber (SMF) transmission.

Low-Timing-Jitter and Low-Phase-Noise Microwave Signal Generation Using a VCSEL-Based Optoelectronic Oscillator

“…Nowadays, a wide range of applications, such as instrumentation (Wang et al, 2020, Feng et al , 2021, physical variable measurement (Zou et al, 2016), and data transmission (Chi et al , 2016), integrate electrical signals in the microwave and mm-wave range into their systems. Electronic oscillators have traditionally been used in telecommunications as high-frequency signal sources.…”